Inheritance (College Board AP® Biology): Exam Questions

A new species of fly was discovered on an island in the South Pacific. Several different crosses were performed, each using 100 females and 100 males. The phenotypes of the parents and the resulting offspring were recorded. 

Cross I: True-breeding bronze-eyed males were crossed with true-breeding red-eyed females. All the F₁ offspring had bronze eyes. F₁ flies were crossed, and the data for the resulting F₂ flies are given in the table below.  

Cross II: True-breeding normal-winged males were crossed with true-breeding stunted-winged females. All the F₁ offspring had stunted wings. F₁ flies were crossed, and the data for the resulting F₂ flies are given in the table below.

Cross III: True-breeding bronze-eyed, stunted-winged males were crossed with true-breeding red-eyed, normal-winged females. All the F₁ offspring had bronze eyes and stunted wings. The F₁ flies were crossed with true breeding red-eyed, normal-winged flies, and the results are shown in the table below. 

What conclusions can be drawn from cross I and cross II? Explain how the data support your conclusions for each cross. 

What conclusions can be drawn from the data from cross III? Explain how the data support your conclusions. 

Identify and discuss TWO different factors that would affect whether the island’s fly population is in Hardy-Weinberg equilibrium for the traits above. 

In a certain species of plant, the diploid number of chromosomes is 4 (2n = 4). Flower color is controlled by a single gene in which the green allele (G) is dominant to the purple allele (g). Plant height is controlled by a different gene in which the dwarf allele (D) is dominant to the tall allele (d). Individuals of the parental (P) generation with the genotypes GGDD and ggdd were crossed to produce F₁ progeny.

Construct a diagram below to depict the four possible normal products of meiosis that would be produced by the F₁ progeny. Show the chromosomes and the allele(s) they carry. Assume the genes are located on different chromosomes and the gene for flower color is on chromosome 1.

Predict the possible phenotypes and their ratios in the offspring of a testcross between an F₁ individual and a ggdd individual.

If the two genes were genetically linked, describe how the proportions of phenotypes of the resulting offspring would most likely differ from those of the testcross between an F₁ individual and a ggdd individual.

In the tongue sole fish (Cynoglossus semilaevis), sex is determined by a combination of genetics and environmental temperature. Genetically male fish have two Z chromosomes (ZZ), and genetically female fish have one Z chromosome and one W chromosome (ZW). When fish are raised at 22^oC, ZZ fish develop into phenotypic males and ZW fish develop into phenotypic females. However, when fish are raised at 28^oC, the Z chromosome is modified (denoted as Z*). Z* W individuals develop as phenotypic males that are fertile and can pass on the Z* chromosome to their offspring even when the offspring are raised at 22^oC. A cross between a ZW female and a Z*Z male is shown in the Punnett square below.

Predict the percent of phenotypic males among the F₁ offspring of the cross shown in the Punnett square if the offspring are raised at 22^oC

At least one Z or Z* chromosome is necessary for survival of the fish. A researcher crossed two fish and observed  a 2: 1 ratio of males to females among the offspring. Based on the information, identify the genotype the male parent in the cross. Describe ONE fitness cost to the female of mating with this particular male.

PDC deficiency is caused by mutations in the PDHA 1 gene, which is located on the X chromosome. A male with PDC deficiency and a homozygous female with no family history of PDC deficiency have a male offspring. Calculate the probability that the male offspring will have PDC deficiency.

Geneticists investigated the mode of inheritance of a rare disorder that alters glucose metabolism and first shows symptoms in adulthood. The geneticists studied a family in which some individuals of generations II and Ill are known to have the disorder. Based on the pedigree (Figure 1), the geneticists concluded that the disorder arose in individual II—2 and was caused by a mutation in mitochondrial DNA.

Figure 1. Pedigree of a family showing individuals with the glucose metabolism disorder. A question mark indicates that the phenotype is unknown

TABLE 1. AVERAGE BLOOD GLUCOSE LEVELS OF INDIVIDUALS IN GENERATION IV

TABLE 2. PHENOTYPIC CLASSIFICATIONS BASED ON BLOOD GLUCOSE LEVELS

The disorder alters glucose metabolism. Describe the atoms AND types of bonds in a glucose molecule.

Using the template in the space provided for your response, construct an appropriately labeled graph based on the data in Table 1. Determine one individual who is both at risk of developing the disorder and has a significantly different blood glucose level from that of individual IV — 1.

Based on the pedigree, identify all individuals in generation IV who can pass on the mutation to their children.

Based on the fact that individual II — 2 is affected, a student claims that the disorder is inherited in an X-Iinked recessive pattern. Based on the student's claim, predict which individuals of generation Ill will be affected by the disorder. Based on the pedigree, justify why the data do NOT support the student's claim.

Researchers are studying the inheritance of a rare neurological disorder in a population of primates. The disorder occurs only in individuals who inherit two copies of a specific allele (a), and is more common in individuals with trisomy 12, a condition caused by nondisjunction during meiosis.

The researchers also compared the DNA sequences of the primates to those of closely related mammal species to study shared ancestry.

(i) Describe the inheritance of this neurological disorder based on Mendelian genetics.

(ii) Explain how trisomy can increase the likelihood of expressing recessive disorders.

(i) Determine the genotypic and phenotypic ratios from a cross between two heterozygous carriers.

(ii) Predict how natural selection might alter the genotypic and phenotypic ratios in this primate population over time.

(iii) Justify your prediction to part (ii)

In a population of primates, individuals living in colder regions develop darker, thicker fur, while those in warmer regions develop lighter, thinner fur, even though they have the same genetic makeup.

Explain how this observation provides evidence for phenotypic plasticity.

(i) Describe how DNA sequences are used to determine relationships.

(ii) Explain why mutations in DNA provide evidence for evolution over time.

A researcher investigates the inheritance of two traits in fruit flies:

• Eye color is a sex-linked trait on the X chromosome, where red (R) is dominant to white (r).

• Wing shape is an autosomal trait, where normal wings (W) are dominant to vestigial wings (w).

A female fly with genotype XᴿXʳ Ww is crossed with a white-eyed male with vestigial wings (XʳY ww). The researcher records the phenotypes of 1,000 male offspring. The results are shown in Table 1.

Table 1. Male offspring phenotypes (n = 1,000)

(i) Describe how sex-linked traits are inherited differently from autosomal traits.

(ii) Explain why the male offspring are used to analyze inheritance in this experiment.

(i) Predict the expected phenotypic ratio in male offspring if the two genes assorted independently.

(ii) Explain how the observed phenotypic ratios differ from the expected ratios under independent assortment.

Analyze the data to determine whether the genes appear linked.

Researchers perform a second cross using the same parent genotypes, but this time they observe equal numbers of all four phenotypes in the male offspring.

(i) Predict what this result suggests about the location of the genes.

(ii) Justify your prediction using principles of inheritance.

Mitochondria and chloroplasts have their own DNA, which is inherited maternally in most organisms. These organelles are transmitted through the egg in animals and the ovule in plants. Therefore, traits caused by mutations in mitochondrial or chloroplast DNA do not follow Mendelian patterns.

Researchers studied a plant species where the green color of leaves is determined by chloroplast genes. They crossed two types of plants:

• A female with yellow leaves (caused by a chloroplast mutation)

• A male with green leaves (normal chloroplasts)

They then performed the reciprocal cross — a green-leafed female crossed with a yellow-leafed male.

Table 1. Leaf color in offspring from reciprocal crosses (n = 100 per cross)

(i) Describe how chloroplast inheritance differs from nuclear gene inheritance.

(ii) Explain why chloroplast traits do not follow Mendel’s laws.

(i) Predict the outcome of a cross between a green-leafed female and a green-leafed male.

(ii) Justify your prediction using your understanding of organelle inheritance.

In this plant species, green leaves allow for more efficient photosynthesis than yellow leaves.

(i) Predict how the frequency of the chloroplast mutation might change in a natural population over time.

(ii) Justify your prediction.

A student proposes that the yellow-leafed trait is caused by a mutation in a nuclear gene.

(i) Predict the expected offspring phenotypes if this were true. Assume that the yellow colour is caused by a recessive allele.

(ii) Explain how these results would differ from those shown in Table 1.

(iii) Justify why this hypothesis is not supported by the data.